1. Field of the Invention
The invention relates to a thermoelectric generator unit comprising at least one thermoelectric module, which is provided with an exhaust gas heat exchanger on one side and a coolant heat exchanger on the opposite side in sandwich-like arrangement, the exhaust gas heat exchanger and the coolant heat exchanger being designed as flat ducts whose flat sides are joined by lateral wall sections.
2. The Prior Art
Thermoelectric generators (TEGs) generating electrical energy by utilizing a temperature difference have been known for quite some time, for instance in the context of motor vehicles where the exhaust gas heat of an internal combustion engine is utilized. The thermoelectric module of such generator units consists of a series of p- and n-doped legs, which are provided with electrical contacts at the ends. The Seebeck effect is exploited, in which the temperature difference between two ends (i.e., a high-temperature section and a low-temperature section) of a piece of metal or semiconductor gives rise to a difference in electric potential.
From DE 10 2005 005 077 A1 there is known a thermoelectric generator for an internal combustion engine which is connected to an exhaust gas duct. The generator has a hot part, which is placed on the exhaust gas duct, and a cold part (coolant heat exchanger), which is connected to the cooling circuit of the internal combustion engine. The individual parts of the thermoelectric generator are placed concentrically about the exhaust gas duct and are pressed against the surface of the exhaust gas duct by single, circular, external holding elements, elastic elements being interposed between coolant heat exchanger elements and the circular holding elements in order to keep the thermoelectric generator elements pressed between the hot parts and the cold parts of the generator in such a way that relative motion between the individual components will be possible due to a difference in thermal expansion of the components. The problem thus is to find a way of uniformly pressing together an arrangement consisting of exhaust gas heat exchanger, thermoelectric module and coolant heat exchanger, thus ensuring good thermal contact while keeping stresses due to different thermal expansion of the components as small as possible to avoid damaging the components.
From DE 10 2005 051 309 A1 there has become known in this context a thermoelectric generator, which has a planar exhaust gas heat exchanger and at least two thermoelectric elements, the exhaust gas heat exchanger being placed sandwich-wise between the two thermoelectric elements. The unit is closed on the outside by two coolant heat exchangers, with the group of exhaust gas heat exchanger plus thermoelectric elements being sandwiched between the two coolant heat exchangers. The coolant heat exchangers are provided with outwardly pointing fastening tongues with pass-through openings. In addition there is provided a central bore through all elements of the generator unit; in the central bore as well as in the pass-through openings bolts with counter-nuts are provided for pressing together and fixing the individual elements. Instead of screws spring clips could be used.
Furthermore there is known from US 2006/0157102 A1 a system for utilizing waste heat, for instance from an internal combustion engine, which is provided with a central high-temperature heat exchanger with an internal lamellar structure in a flat assembly, thermoelectric modules being placed on both sides. The outer side of each thermoelectric module is in thermal contact with a low-temperature heat exchanger, which also has an internal lamellar structure. The hot exhaust gas in the high-temperature heat exchanger and the coolant in the low-temperature heat exchanger are fed through the thermo-electric generator unit in parallel but oppositely directed flows.
From JP 2007-221895 a thermoelectric generator unit shown in FIG. 1 is known, whose thermoelectric modules are in contact with an exhaust gas heat exchanger (high-temperature heat exchanger) on one side, and with a coolant heat exchanger (low-temperature heat exchanger) on the other side. The coolant heat exchanger and the exhaust gas heat exchanger are configured as flat ducts, such that the individual components may be stacked and thus manufactured in a space-saving design.
The whole assembly is held together by a plurality of two-part clamping elements, and to protect the TEG-modules from corrosion a heat-resistant waterproof frame is provided, which is inserted into opposing grooves of the exhaust gas- and coolant heat exchangers. Between the clamping elements and the heat exchangers lying on the outside of the unit spring elements configured as disk springs are provided, by which the pressing force may be adjusted.
From DE 15 39 330 A1 a thermoelectric generator unit is known whose thermoelectric modules are thermo-legs with electrical contact bridges, which on the hot side contact a large-volume heat exchanger pipe and on the cold side are in contact with a plurality of flat ducts distributed over the periphery. The flat ducts can be elastically deformed in the direction of the axis of the thermo-legs in order to compensate for manufacturing tolerances and changes in length due to the temperature differences arising. The flat ducts are attached on the central heat exchanger pipe by means of brackets and screws provided on both sides of the flat ducts.
It is an object of the present invention to propose a thermoelectric generator unit which is based on the energy generator devices described above and which exhibits great simplicity of design, permitting the individual structural elements of the generator unit to be uniformly and lastingly pressed against each other in a simple manner.